Squamous cell carcinoma of the head and neck (SCCHN) at oral an oropharyngeal sites (OSCC) is the sixth most frequent cancer worldwide. Known etiologic factors in OSCC include tobacco and alcohol. OSCC is amenable to pathogenetic examination because the regions surrounding primary tumors often are characterized by foci of dysplasia (preneoplastic lesions, PN), carcinoma in situ, and/or OSCC. The goal of this detailed, multifaceted genetic analysis is to test the hypothesis that specific genetic changes in six regions of the human genome (that are frequently altered in SCCHN) are involved in the pathogenesis of OSCC. Our goal is to identify early genetic changes that predict progression to malignancy in the nontumorous but dysplastic mucosa (PN) surrounding primary OSCC. We will use the more than 200 new patients and 2500 patients followed after diagnosis of primary SCCHN in our center annually to satisfy the following Specific Aims. 1) To examine consistent genetic changes in PN and OSCC that point to key genes in OSCC pathogenesis and progression, focusing on chromosome regions 1p, 3p, 7q, chromosome 11, and the RB1 and TP53 genes in 150 matched pairs of dysplastic/PN lesions and tumors by a) classical cytogenetic analysis; b) interphase molecular cytogenetic analysis using in situ hybridization with chromosome-and chromosome region-specific DNA probes; c) loss of heterozygosity using a panel of highly informative DNA markers; d) examining TP533 mutations using a combination of immunocytochemistry, single strand conformational polymorphism (SSCP) analysis of the gene, and direct sequencing of highly conserved exons 5 through 8; e) identifying human papillomavirus (HPV) status and type in light of the role of the HPV E6 protein in abrogating p53 function. 20 To identify which of the genetic factors described above are predictive of tumor development in PN lesions and in OSCC, prognostic of clinical course, metastasis, and survival, by correlating the results of the genetic studies with diagnosis, disease stage, histopathology, exposure history, response to therapy, and clinical outcome. These early genetic changes, predictive of progression to malignancy can then be tested in the larger group of patients with preneoplastic lesions with lower malignant potential (leukoplakia, erythroplakia, etc.) or in the normal mucosa of high risk individuals (i.e., heavy smokers) to identify those individuals at highest risk for tumor formation and target this group for preventive intervention (surgery, chemoprevention, behavior modification, etc.)